Felt with cellulosic fibers for forming fiber cement articles

ABSTRACT

A fiber cement felt includes: a base fabric layer including machine direction yarns (MD yarns) and cross-machine direction yarns (CMD yarns); and one or more batt layers overlying the base fabric layer. One of the MD yarns, CMD yarns, and batt layer includes erodible cellulosic fibers.

RELATED APPLICATION

The present application claims the benefit of and priority from U.S. Provisional Patent Application No. 61/914,165, filed Dec. 10, 2013, the disclosure of which is hereby incorporated herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to fabrics, and more particularly to fabrics employed to form articles of fiber cement.

BACKGROUND OF THE INVENTION

Fiber cement is a well-known material employed in many building components, such as siding, roofing and interior structures, as well as pipes, particularly for waste water transport. Fiber cement typically comprises a mixture of cement (i.e., lime, silica and alumina), clay, a thickener, inorganic fillers such as calcium carbonate, and one or more fibrous materials. In the past, asbestos was commonly included as the fibrous material (see U.S. Pat. No. 4,216,043 to Gazzard et al.); because of the well-documented problems asbestos presents, now fiber cement typically includes a natural or synthetic fiber, such as acrylic, aramid, polyvinyl alcohol, polypropylene, cellulose or cotton. Fiber cement is popular for the aforementioned applications because of its combination of strength, rigidity, impact resistance, hydrolytic stability, and low thermal expansion/contraction coefficient.

To be used in siding or roofing components, fiber cement is often formed in sheets or tubes that can be used “as is” or later cut or otherwise fashioned into a desired shape. One technique of forming fiber cement articles (known as the Hatschek process) involves creating an aqueous fiber cement slurry of the components described above, depositing the slurry as a thin sheet or web on a porous fabric belt, and conveying the slurry over and through a series of rollers to flatten and shape the slurry. As the slurry is conveyed, moisture contained therein drains through openings in the fabric. Moisture removal is typically augmented by the application of vacuum to the slurry through the fabric (usually via a suction box located beneath the porous fabric). After passing through a set of press rolls, the fiber cement web can be dried and cut into individual sheets, collected on a collection cylinder for subsequent unrolling and cutting into individual sheets, or collected as a series of overlying layers on a collecting cylinder that ultimately forms a fiber cement tube.

The porous fabric used to support the slurry as moisture is removed is typically woven from very coarse (between about 2500 and 3000 dtex) polyamide yarns. Most commonly, the yarns are woven in a “plain weave” pattern, although other patterns, such as twills and satins, have also been used. Once they are woven, the yarns are covered on the “sheet side” of the fabric (i.e., the side of the fabric that contacts the fiber cement slurry) with a batt layer; on some occasions, the “machine side” of the fabric (i.e., the side of the fabric that does not contact the slurry directly) is also covered with a batt layer. The batt layer assists in the retrieval, or “pick-up,” of the slurry from a vat or other container for processing. Because of the presence of the batt layer(s), the fabric is typically referred to as a fiber cement “felt.”

The lifetime of a fiber cement felt is typically relatively short; it is not unusual for a fiber cement felt to last only 1-2 weeks. Also, typically a fiber cement felt requires some start-up time (approximately 6-10 hours) before it is suitable for manufacturing at full speed. The start-up process of a fiber cement felt compacts the felt, which is necessary in order to manufacture a consistent product. Given the short lifetime of fiber cement felts and the comparatively long start-up period, it may be desirable to provide a fiber cement felt that reduces or largely eliminates the start-up procedure.

SUMMARY OF THE INVENTION

As a first aspect, embodiments of the invention are directed to a fiber cement felt, comprising: a base fabric layer including machine direction yarns (MD yarns) and cross-machine direction yarns (CMD yarns); and one or more batt layers overlying the base fabric layer. One of the MD yarns, CMD yarns, and batt layer includes erodible cellulosic fibers.

As a second aspect, embodiments of the invention are directed to a fiber cement felt, comprising: a base fabric layer including MD yarns and CMD yarns; and one or more batt layers overlying the base fabric layer. One of the MD yarns, CMD yarns, and batt layer includes erodible hydrophilic fibers.

As a third aspect, embodiments of the invention are directed to a fiber cement felt, comprising: a base fabric layer including MD yarns and CMD yarns; and one or more batt layers overlying the base fabric layer. One of the MD yarns, CMD yarns, and batt layer includes hydrophilic cellulosic fibers.

As a fourth aspect, embodiments of the invention are directed to a method of manufacturing fiber cement, comprising the steps of:

-   -   (b) providing a fiber cement felt, comprising: a base fabric         layer including MD yarns and CMD yarns; and one or more batt         layers overlying the base fabric layer; wherein one of the MD         yarns, CMD yarns, and batt layer includes cellulosic fibers;     -   (b) positioning the fiber cement felt on a series of support         rolls of a fiber cement forming machine;     -   (c) depositing a fiber cement slurry on the fiber cement felt;     -   (d) removing moisture from the slurry to form a fiber cement         web;     -   (e) during steps (c) and/or (d), allowing the cellulosic fibers         to erode from the felt; and     -   (f) repeating step (d) while substantially all of the cellulosic         fibers have been eroded.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustration of a fiber cement forming apparatus according to embodiments of the present invention.

FIG. 2 is a top perspective view of a portion of a base fabric of a fiber cement felt according to embodiments of the present invention, with CMD yarns shown extending in the horizontal direction and MD yarns shown extending in the vertical direction.

FIG. 3 is a schematic section view of a fiber cement felt that includes the base fabric of FIG. 2.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention will now be described more fully hereinafter, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements throughout. Thicknesses and dimensions of some components may be exaggerated for clarity.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein the expression “and/or” includes any and all combinations of one or more of the associated listed items.

As used herein, the terms machine direction (“MD”) and cross machine direction (“CMD”) refer, respectively, to a direction aligned with the direction of travel of the felt on the fiber cement machine, and a direction parallel to the fabric surface and traverse to the direction of travel.

In addition, spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. Thus, the exemplary term “under” can encompass both an orientation of over and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Well-known functions or constructions may not be described in detail for brevity and/or clarity.

Referring now to FIG. 1, a fiber cement forming apparatus, designated broadly at 10, is illustrated therein. The forming apparatus 10, which performs a typical Hatschek process, generally includes an endless fiber cement felt 30 positioned in rolling contact with and driven by a number of guide rolls 20. Beginning in the lower right corner of FIG. 1, the felt 30 passes above three vats 12, each of which contains a batch of fiber cement slurry 14. As used herein, “fiber cement” means any cementitious composition including cement, silica, and fiber for reinforcement, including asbestos, polyvinyl alcohol, polypropylene, cotton, wood or other cellulosic material, acrylic, and aramid. It is contemplated that other materials such as thickeners, clays, pigments, and the like, that impart desirable processing or performance characteristics to the fiber cement slurry 14 or an article formed therefrom may also be included. Each vat 12 is positioned below a deposition cylinder 16 mated with a couch roll 18. Each vat 12 also includes an agitator 13 that prevents the fiber cement slurry 14 from solidifying therein.

Rotation of each deposition cylinder 16 collects fiber cement slurry 14 on the cylinder's surface; as the felt 30 travels over and contacts the cylinder 16, the slurry 14 is transferred from the cylinder 16 to the felt 30. The amount of slurry 14 deposited on the fabric 30 by each cylinder 16 is controlled by the corresponding couch roll 18. Preferably, the fiber cement slurry 14 is deposited as a web 21 at a thickness of between about 0.3 mm and 3 mm.

Still referring to FIG. 1, once the fiber cement slurry web 21 has been collected on the felt 30 from each of the vats 12, the felt 30 conveys the slurry web 21 over one guide roll 20, then over one or more suction boxes 26 (two are shown in FIG. 1), each of which applies negative pressure to the felt 30, thereby encouraging the removal of moisture from the slurry web 21. Finally, the felt 30 and the slurry web 21 pass over a second guide roll 20, then between the nip formed by a breast roll 24 and a forming roll 22. After passing through the nip, the slurry web 21 has formed into a semi-solid fiber cement sheet 28 that is collected on the surface of the forming roll 22.

Those skilled in this art will recognize that other forming apparatus are also suitable for use with the fiber cement felts of the present invention. For example, felts of the present invention can also be used to form fiber cement pipe. In such an operation, the fiber cement sheet 28 can be collected in contacting layers on a forming roll; as they dry, the overlying layers form a unitary laminated tube. Often, a pipe forming apparatus will include small couch rolls that act in concert with the forming roll to improve interlaminar strength. Also, a second felt may travel over the additional couch rolls to assist in water absorption and finishing.

A portion of an exemplary base fabric for a fiber cement felt 30, designated broadly at 40, is shown in FIG. 2. The fabric 40 includes MD yarns 41 and CMD yarns 42 interwoven with each other in a plain weave pattern (i.e., an “over 1/under 1” pattern). This pattern repeats itself over the expanse of the fabric 40. Those skilled in this art will appreciate that other configurations for the base fabric may be employed, including multi-layer fabrics and multiple fabric layers; other exemplary base fabrics are illustrated and described in U.S. Pat. No. 5,891,516 and U.S. Patent Publication Nos. 2005/0085148, 2006/0068665, 2007/0155272, 2007/0215230, 2012/0098161, and 2013/0008552, the disclosure of each of which is hereby incorporated herein in its entirety.

As shown in FIG. 3, the felt 30 also includes a top batt layer 52 that overlies the fabric 40 and a bottom batt layer 54 that underlies the fabric 40. The batt layers 52, 54 may be formed of material that assists in taking up fiber cement slurry 14 from the vats 12 to form the fiber cement web 21 in FIG. 1.

In fiber cement felts according to one embodiment of the invention, the top and/or bottom batt layers 52, 54 may comprise cellulosic fibers. The term “cellulosic fiber” can be any of numerous cellulosic fibers known to those skilled in this art, including viscose, acetate, cupro, lyocell, reconstituted cellulose, and the like. In some embodiments, the batt layers 52, 54 may be formed of 100 percent cellulosic fibers, or may include other materials, such as a synthetic fiber like acrylic, aramid, polyester, or polyamide, or a natural fiber such as wool, that assists in taking up fiber cement slurry 14.

In certain embodiments, the cellulosic fibers may be included in the batt layer in an amount between about 5 and 95 percent by weight, with between about 20 and 35 percent by weight being particularly suitable. In such embodiments, the remainder of the batt layers 52, 54 may be formed of or include polyamide. The cellulosic fibers may be relatively fine (between about 1 and 10 dtex, typically about 5 to 7 dtex), and typically have a tensile strength of between about 15 and 40 cN/tex.

It has been found that, when cellulosic fibers as described above are included in the top batt layer 52 of a fiber cement felt 40, the start-up procedure typically required by fiber cement felts can be reduced or even, in some cases, eliminated. A typical start-up procedure entails positioning the fiber cement felt on a fiber cement forming machine, placed in tension, and operated until it runs straight (i.e., in alignment with the direction of travel). The felt is then wetted with low pressure showers and run through a number of revolutions. At this point the felt is ready to accept slurry for manufacturing; however, until then the slurry tends to fall from the underside of the felt, such that fiber cement is not formed.

According to embodiments of the present invention, the start-up procedure can be decreased or, in some cases, eliminated. In other words, the wetting of the felt with the low pressure showers and subsequent operation prior to the application of slurry can be omitted. The hydrophilicity of the cellulosic fibers assists with pick-up of the slurry on the underside of the felt. Thus, the fiber cement felt machine can be operated within a short time of installation of the felt on the machine

While not wishing to be bound by any theory of operation, the inventors speculate that the cellulosic fibers described above, which tend to be denser than the typical fibers used in batt layers, can help to “pre-compact” the felt, thereby reducing or eliminating the need to compact the felt prior to operation. Also, the cellulosic fibers are sufficiently brittle that they tend to wear or erode from the top batt layer 52 soon after operation begins (often within about 2 to 3 hours, or within 24 hours for substantially all of the cellulosic fibers to wear away), during which time the remainder of the material comprising the felt becomes compacted. After the cellulosic fibers have worn or eroded from felt, the felt 40 is compacted and is suitable for continued manufacturing. As used herein, an “erodible” material is one that erodes or wears away to the extent that less than about 5 percent of the original material remains.

It should be noted that, if the cellulosic fibers did not erode or wear away from the felt, once the remainder of the felt was compacted, the presence of the cellulosic fibers could cause plugging in the felt, which would negatively impact drainage. Thus, in some embodiments the sacrificial nature of the cellulosic fibers is beneficial.

Alternatively, or in addition, the inventors speculate that the hydrophilicity of the cellulosic fibers (which are more hydrophilic than polyamide and other materials often employed as a material in batt fibers) assists the felt in taking up water during the early phases of operation. This behavior can also assist the felt in performing suitably for manufacturing without a typical start-up procedure. A material having a water absorption of between about 10 and 35 percent may be suitable for use in felts according to embodiments of the invention,

Other materials that may be suitable substitutes for cellulosic fibers include wool, polyvinyl acrylate (PVA) and cotton.

In some embodiments, it may be beneficial for the felt 40 to include cellulosic or similar fibers in fiber yarns that form the base fabric of the felt. Thus, the MD yarns 41, the CMD yarns 42, or both the MD yarns 41 and the CMD yarns 42 may include cellulosic fiber as a component.

Table 1 below lists the materials for an exemplary fiber cement felt according to embodiments of the invention.

TABLE 1 Component Composition MD yarns Multifilament (1,700 tex) and spunbond (600 tex) - 3.1 ends per cm CMD yarns Spunbond (1,000 tex) - 1.7 ends per cm Top Batt Layer Hydrophilic fibers (30 percent), 22 dtex polyamide fibers (35 percent) and 44 dtex fibers (35 percent) at a layer weight of about 150-200 gsm Bottom Batt Layer 44 dtex polyamide fibers (50 percent) and 70 dtex polyamide fibers (50 percent) at a layer weight of about 300-400 gsm

The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein. 

That which is claimed is:
 1. A fiber cement felt, comprising: a base fabric layer including machine direction yarns (MD yarns) and cross-machine direction yarns (CMD yarns); and one or more batt layers overlying the base fabric layer; wherein one of the MD yarns, CMD yarns, and batt layer includes erodible cellulosic fibers.
 2. The fiber cement felt defined in claim 1, wherein the erodible cellulosic fibers are included in the batt layer.
 3. The fiber cement felt defined in claim 2, wherein the erodible cellulosic fibers comprise between about 5 and 95 percent by weight of the batt layer.
 4. The fiber cement felt defined in claim 2, wherein the erodible cellulosic fibers are sized between about 3 and 7 dtex.
 5. The fiber cement felt defined in claim 2, wherein the erodible cellulosic fibers have a water absorption of between about 10 and 35 percent.
 6. A fiber cement felt, comprising: a base fabric layer including machine direction yarns (MD yarns) and cross-machine direction yarns (CMD yarns); and one or more batt layers overlying the base fabric layer; wherein one of the MD yarns, CMD yarns, and batt layer includes erodible hydrophilic fibers.
 7. The fiber cement felt defined in claim 6, wherein the erodible hydrophilic fibers are included in the batt layer.
 8. The fiber cement felt defined in claim 7, wherein the erodible hydrophilic fibers have a water absorption of between about 10 and 35 percent.
 9. The fiber cement felt defined in claim 7, wherein the erodible hydrophilic fibers comprise between about 5 and 95 percent by weight of the batt layer.
 10. The fiber cement felt defined in claim 6, wherein the erodible hydrophilic fibers are sized between about 3 and 7 dtex.
 11. A fiber cement felt, comprising: a base fabric layer including machine direction yarns (MD yarns) and cross-machine direction yarns (CMD yarns); and one or more batt layers overlying the base fabric layer; wherein one of the MD yarns, CMD yarns, and batt layer includes hydrophilic cellulosic fibers.
 12. The fiber cement felt defined in claim 11, wherein the hydrophilic cellulosic fibers are included in the batt layer.
 13. The fiber cement felt defined in claim 12, wherein the hydrophilic cellulosic fibers have a water absorption of between about 10 and 35 percent.
 14. The fiber cement felt defined in claim 12, wherein the hydrophilic cellulosic fibers comprise between about 5 and 95 percent by weight of the batt layer.
 15. The fiber cement felt defined in claim 12, wherein the hydrophilic cellulosic fibers are sized between about 3 and 7 dtex.
 16. A method of manufacturing fiber cement, comprising the steps of: (a) providing a fiber cement felt, comprising: a base fabric layer including machine direction yarns (MD yarns) and cross-machine direction yarns (CMD yarns); and one or more batt layers overlying the base fabric layer; wherein one of the MD yarns, CMD yarns, and batt layer includes cellulosic fibers; (b) positioning the fiber cement felt on a series of support rolls of a fiber cement forming machine; (c) depositing a fiber cement slurry on the fiber cement felt; and (d) removing moisture from the slurry to form a fiber cement web; (e) during steps (c) and/or (d), allowing the cellulosic fibers to erode from the felt; and (f) repeating step (d) while substantially all of the cellulosic fibers have been eroded.
 17. The method defined in claim 16, wherein step (e) is completed within 24 hours of operation.
 18. The method defined in claim 16, wherein the cellulosic fibers are included in the batt layer.
 19. The method defined in claim 18, wherein the cellulosic fibers have a water absorption of between about 10 and 35 percent.
 20. The method defined in claim 18, wherein the cellulosic fibers comprise between about 5 and 95 percent by weight of the batt layer.
 21. The method defined in claim 18, wherein the cellulosic fibers are sized between about 3 and 7 dtex. 